In order to prevent occurrence of a failure of electronic equipment due to abnormal heating of a pack battery used in electronic equipment such as mobile telephones, it is required that a temperature fuse be mounted on the pack battery. It is also required that a current fuse be mounted on electronic equipment to prevent occurrence of a failure due to abnormal current.
In a conventional temperature fuse, a fuse element which melts down when it reaches a predetermined temperature is provided at its both ends with terminal portions and the terminal portions are connected to a circuit such as a power supplying circuit. When abnormal heating is produced in a component constituting a power supply or the like (such as a battery), the fuse element serves its function at a high temperature caused by the abnormal heating. Thus, the temperature fuse is adapted to break the circuit to prevent the internal components and the like from being damaged.
In the conventional fuse, a fuse element made of a fusible member is welded to a pair of lead terminals so as to span the same, and thereby, it is electrically connected to the lead terminals. Fuses of the described type are disclosed in, for example, Japanese Unexamined Patent Publication No. H11-273520 and Japanese Unexamined Patent Publication No. 2002-33035. In those cases, an intermediate layer for welding is provided between the fuse element and the lead terminal for ensuring good welding of the fuse element to the lead terminal.
FIG. 11 is a lateral sectional view of a prior art fuse. FIG. 12 is a lateral sectional view of fuse element 104 as have been melted down. The fuse is constructed by disposing a pair of lead terminals 100 on substrate 103 and by welding fuse element 104 to lead terminals 100 through plated layer 101 provided on the surface of lead terminals 100. Though it is not shown, some flux or a cover may be provided on fuse element 104. A fuse is manufactured in the following way. First, a pair of lead terminals 100 are disposed on substrate 103. Then, plated layers 101 are formed on the pair of lead terminals 100 arranged as above. At this time, plated layers 101 are formed so far as they are even spread on opposing faces 102 of lead terminals 100. Fuse element 104 is placed on plated layers 101 and pressed and heated from its upper side to be welded to plated layers 101. A fuse is manufactured through the above described steps.
However, in the prior art fuse, plated layers 101 are formed to be extended over opposing faces 102. Therefore, when fuse element 104 is welded, spread-out portions 105 thereof are formed on the opposing portions so that the insulation distance between lead terminals 100 opposing each other is shortened. Furthermore, when fuse element 104 is melted down, melted fuse element 104 is spread out over opposing faces 102, whereby large spread-out portions 105 are formed as shown in FIG. 12. Then, the insulation distance between opposing lead terminals 100 becomes still shorter after the melting down of the fuse element. Hence, insulating capability becomes insufficient though the fuse element is melted down.
In a case of a large sized fuse, it is no problem if there exist spread-out portions 105 because lead terminals 100 originally have a large face-to-face distance. However, in these days, electronic equipment is becoming increasingly smaller in size and lower in profile. Also with respect to batteries having fuses mounted thereon, advances are being made in making them lower profiled and smaller sized. This makes it indispensable to make the fuse smaller sized and lower profiled and it is naturally required to narrower the face-to-face distance of lead terminals 100. However, there is a limit in making the face-to-face distance narrower due to the deterioration of insulating capability caused by existence of spread-out portions 105. Hence, it is required to previously provide a sufficiently large face-to-face distance. As a result, it becomes impossible to make the fuse smaller sized and lower profiled.